I used to own one of these....so I am just going to throw this out there for you.
As with most amps, when you bridge two channels to one, the rated output jumps dramatically, sometimes even on the order of doubling the power. This is not true for the MC431. It is rated at 100w/channel at 12v RMS. When you bridge two channels, the power is exactly the sum, or 200w at 12v RMS.
This was confirmed to me by a McIntosh rep and is also stated in the Owners Manual.
No other McIntosh amps have this same "summation" as far as I know.
The silver lining in this, is that McIntosh amps are tested and rated at 12v and they are often underrated in their power output versus the actual output you will see.
Now is the time to tell me you are not bridging this amp and all of the above does not matter to you.